It is known that most bottles are closed by a cap which screws onto the neck or spout, a liquid-tight seal being placed between the upper part of the neck of the bottle and the inside ring of the cap. Closure is obtained by a helical movement (rotating plus translation), of the cap on the neck. During the closing of the bottle the seal flattens, thus braking the translation movement whilst the rotary movement can continue as a function of the force couple exerted on the cap. It is found that in relation to the body of the bottle, the rotational orientation of the cap when the bottle is fully closed can vary over an angle which is of the order of 90.degree., this angle depending of course on the pitch of the thread and the compressibility of the seal.
This fact is not a significant disadvantage when the cap and the bottle are rotationally symmetrical. It is not the same when the bottle and/or the cap have polygonal sections, for example, square ones. More often than not in that case the cap is out of line, which distinctly spoils the appearance of the whole.
In the perfume industry, the product in the bottle being by definition very volatile, it is essential to arrange for a closure which ensures a perfect fit. To this end, it has been known to arrange inside the cap proper a skirt with external fluting and internal threading which, by resilient deformation absorbs the differences in dimensions arising from manufacture and ensures fluid-tightness by close contact with the material of the bottle.